From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Gavin Shan <gshan@redhat.com>, linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org, catalin.marinas@arm.com,
will@kernel.org, akpm@linux-foundation.org, shan.gavin@gmail.com,
chuhu@redhat.com
Subject: Re: [PATCH 00/12] mm/debug_vm_pgtable: Enhancements
Date: Mon, 12 Jul 2021 09:44:46 +0530 [thread overview]
Message-ID: <42a26202-10f7-e744-3fc5-c9e5a7445193@arm.com> (raw)
In-Reply-To: <20210706061748.161258-1-gshan@redhat.com>
Hi Gavin,
Though I have not jumped into the details for all individual
patches here but still have some high level questions below.
On 7/6/21 11:47 AM, Gavin Shan wrote:
> There are couple of issues with current implementations and this series
> tries to resolve the issues:
>
> (a) All needed information are scattered in variables, passed to various
> test functions. The code is organized in pretty much relaxed fashion.
All these variables are first prepared in debug_vm_pgtable(), before
getting passed into respective individual test functions. Also these
test functions receive only the required number of variables not all.
Adding a structure that captures all test parameters at once before
passing them down will be unnecessary. I am still wondering what will
be the real benefit of this large code churn ?
>
> (b) The page isn't allocated from buddy during page table entry modifying
> tests. The page can be invalid, conflicting to the implementations
> of set_{pud, pmd, pte}_at() on ARM64. The target page is accessed
> so that the iCache can be flushed when execution permission is given
> on ARM64. Besides, the target page can be unmapped and access to
> it causes kernel crash.
Using 'start_kernel' based method for struct page usage, enabled this
test to run on platforms which might not have enough memory required
for various individual test functions. This method is not a problem for
tests that just need an aligned pfn (which creates a page table entry)
not a real struct page.
But not allocating and owning the struct page might be problematic for
tests that expect a real struct page and transform its state via set_
{pud, pmd, pte}_at() functions as reported here.
>
> "struct vm_pgtable_debug" is introduced to address issue (a). For issue
> (b), the used page is allocated from buddy in page table entry modifying
> tests. The corresponding tets will be skipped if we fail to allocate the
> (huge) page. For other test cases, the original page around to kernel
> symbol (@start_kernel) is still used.
For all basic pfn requiring tests, existing 'start_kernel' based method
should continue but allocate a struct page for other tests which change
the passed struct page. Skipping the tests when allocation fails is the
right thing to do.
- Anshuman
next prev parent reply other threads:[~2021-07-12 4:14 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-06 6:17 [PATCH 00/12] mm/debug_vm_pgtable: Enhancements Gavin Shan
2021-07-06 6:17 ` [PATCH 01/12] mm/debug_vm_pgtable: Introduce struct vm_pgtable_debug Gavin Shan
2021-07-14 6:24 ` Anshuman Khandual
2021-07-19 5:39 ` Gavin Shan
2021-07-20 7:02 ` Anshuman Khandual
2021-07-20 23:07 ` Gavin Shan
2021-07-21 4:20 ` Anshuman Khandual
2021-07-06 6:17 ` [PATCH 02/12] mm/debug_vm_pgtable: Use struct vm_pgtable_debug in basic tests Gavin Shan
2021-07-06 6:17 ` [PATCH 03/12] mm/debug_vm_pgtable: Use struct vm_pgtable_debug in leaf and savewrite tests Gavin Shan
2021-07-06 6:17 ` [PATCH 04/12] mm/debug_vm_pgtable: Use struct vm_pgtable_debug in protnone and devmap tests Gavin Shan
2021-07-06 6:17 ` [PATCH 05/12] mm/vm_debug_pgtable: Use struct vm_pgtable_debug in soft_dirty and swap tests Gavin Shan
2021-07-06 6:17 ` [PATCH 06/12] mm/debug_vm_pgtable: Use struct vm_pgtable_debug in migration and thp tests Gavin Shan
2021-07-06 6:17 ` [PATCH 07/12] mm/debug_vm_pgtable: Use struct vm_pgtable_debug in PTE modifying tests Gavin Shan
2021-07-06 6:17 ` [PATCH 08/12] mm/debug_vm_pgtable: Use struct vm_pgtable_debug in PMD " Gavin Shan
2021-07-06 6:17 ` [PATCH 09/12] mm/vm_debug_pgtable: Use struct vm_pgtable_debug in PUD " Gavin Shan
2021-07-06 6:17 ` [PATCH 10/12] mm/debug_vm_pgtable: Use struct vm_pgtable_debug in PGD and P4D " Gavin Shan
2021-07-06 6:17 ` [PATCH 11/12] mm/debug_vm_pgtable: Remove unused code Gavin Shan
2021-07-06 6:17 ` [PATCH 12/12] mm/debug_vm_pgtable: Fix corrupted page flag Gavin Shan
2021-07-12 4:14 ` Anshuman Khandual [this message]
2021-07-13 1:20 ` [PATCH 00/12] mm/debug_vm_pgtable: Enhancements Gavin Shan
2021-07-14 5:26 ` Anshuman Khandual
2021-07-15 5:17 ` Gavin Shan
2021-07-18 6:36 ` Anshuman Khandual
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